The present invention relates to a method of forming an insulating film, more particularly, a method of forming a low dielectric constant insulating film by a coating method. The invention further relates to a process for producing a semiconductor device using the insulating film as an interlayer dielectric.
In semiconductor devices, wiring resistance and wiring capacitance are increasing steadily with the trend toward wiring size reduction, and this is coming to considerably influence the operating frequency and power consumption of devices. Investigations are hence being made enthusiastically on the use of organosilicon oxide films or organic films formed from a coating fluid as interlayer dielectrics in order to reduce the wiring capacitance and attain higher speed device operation. Such organic films are advantageous in that they have a lower dielectric constant than silicon oxide films formed by the plasma CVD method (p-SiO2; k=4.1) and fluorine-containing silicon oxide films formed by the method (FSG; k=3.3-3.8). However, the organic films each have both merits and demerits as compared with the p-SiO2 and FSG which have hitherto been used, and there are various problems which should be overcome in order to use such organic films as interlayer dielectrics in LSI""s.
An organosilicon oxide film is usually formed by the following procedure. First, an organic solvent solution (varnish) of a polymer having a relatively low molecular weight, e.g., about 1,000 to 10,000, is applied to a substrate, and the coating is dried to remove the organic solvent. Thereafter, the polymer is thermally polymerized to form an organosilicon oxide film. The film thus obtained has poor cracking resistance and, hence, it has been difficult to use this film as a single-layer interlayer dielectric in LSI""s. Polymethylsilsesquioxane (MSQ) films, for example, have a dielectric constant as low as from 2.5 to 3.0 and are expected to be applied to high-performance high-speed semiconductor devices. However, the modulus of elasticity of the MSQ films is 4 GPa, which is far lower than the modulus of elasticity of the related-art CVD silicon oxide films, which is 70 GPa. Because of this, it has been exceedingly difficult to use organosilicon oxide films in a wide range of applications as an interlayer dielectric for multilayered wiring structures comprising five or more layers for use in high-performance semiconductor devices.
The invention has been achieved under the circumstances described above.
One object of the invention is to provide a method of forming an insulating organosilicon oxide film having low dielectric constant and high cracking resistance by a coating method.
Another object of the invention is to provide a process for producing a semiconductor device which is reduced in wiring capacitance and power consumption and can be operated at high speed.
In order to eliminate the problem described above, the invention provides a method of forming an insulating film, which comprises the steps of:
dissolving in a solvent a first polymer and a second polymer which each comprise methylpolysiloxane as the main component and one of which has a weight average molecular weight at least 10 times the weight average molecular weight of the other to thereby prepare a chemical solution;
applying the chemical solution to a semiconductor substrate to form a coating film; and
heat-treating the coating film, thereby forming an organosilicon oxide film.
The invention further provides a process for producing a semiconductor device, which comprises the steps of:
dissolving in a solvent a first polymer and a second polymer which each comprise methylpolysiloxane as the main component and one of which has a weight average molecular weight at least 10 times the weight average molecular weight of the other to thereby prepare a chemical solution;
applying the chemical solution to a semiconductor substrate having elements arranged thereon to form a coating film;
heat-treating the coating film, thereby forming an interlayer dielectric comprising an organosilicon oxide film; and
forming a wiring on the interlayer dielectric.